A fluorohydrocarbon compound exhibits excellent etching selectivity with respect to the etching target material, and has been used as a dry etching gas for producing a semiconductor device.
A fluorohydrocarbon compound used in the semiconductor production field and the like must be purified to have an organic component purity of 99.90% or more and a water concentration of 50 ppm or less in order to achieve high etching selectivity. Such a fluorohydrocarbon compound may be dehydrated using an MS that is a common dehydrating agent.
However, isomerization and a decomposition reaction easily occur when a fluorohydrocarbon compound is brought into contact with an MS, whereby the purity of the fluorohydrocarbon compound may decrease.
For example, Patent Literature 1 proposes a method that purifies hexafluoro-1,3-butadiene (C4F6) using an MS having an average pore size of 5 Å. Patent Literature 1 discloses bringing hexafluoro-1,3-butadiene into contact with the MS using a circulation method, and states that hexafluoro-1,3-butadiene having a purity of at least 99.9% and a water content of 100 ppm or less can be obtained.
However, Patent Literature 1 discloses only an example in which an unsaturated fluorohydrocarbon compound having 4 carbon atoms is used.
Patent Literature 2 proposes a method for purifying a fluorohydrocarbon that includes bringing a fluorohydrocarbon compound having 4 to 8 carbon atoms into contact with an MS or alumina to reduce the hydrogen fluoride content. Patent Literature 2 states that the purity of the compound did not change due to the treatment with the MS, and the production of a decomposition product was not observed (see the examples of Patent Literature 2). Patent Literature 2 discloses 1,1,1,2,4,4,4-heptafluoro-n-butane and 1,1,1,2,2,3,5,5,5-nonafluoro-n-pentane as specific examples of the fluorohydrocarbon compound. However, Patent Literature 2 discloses only examples in which octafluorocyclopentene or 1,1,2,2,3,3,4-heptafluorocyclopentane (i.e., cyclic compound) is used, and does not disclose an example in which a linear compound is used. Paragraph 0023 of Patent Literature 2 states that “molecular sieves 4A and 5A are most preferable”, and a molecular sieve 4A or 5A is used in the examples of Patent Literature 2.
Patent Literature 3 proposes a method that dehydrates a compound while suppressing the occurrence of a decomposition reaction of an organic liquid by utilizing a molecular sieve MS3A for which the amount of acid sites has been reduced to be equal to or less than a specific value through a pretreatment. However, Patent Literature 3 discloses only examples in which an alcohol compound is used.